J - Mobius Inversion Theorem Gym - 101755J

最新推荐文章于 2024-02-11 14:28:55 发布

囧九

最新推荐文章于 2024-02-11 14:28:55 发布

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本文链接：https://blog.youkuaiyun.com/qq_32193741/article/details/81302437

本文探讨了如何从给定长度的棍子中尽可能多地同时组装平行四边形的问题，提出了一个有效的算法来计算可以组装的最大平行四边形数量。

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Statements

There are n sticks, the i-th of which has length ai. Alex wants to assemble from them as many parallelograms as possible simultaneously, with each stick used at most in one parallelogram. What maximal number of parallelograms is it possible to assemble?

Input

The first line contains a single integer n (1 ≤ n ≤ 200000) — the number of sticks.

The second line contains n integers ai (1 ≤ ai ≤ 200000) — the lengths of sticks.

Output

Output a single integer — the maximal number of parallelograms that is possible to assemble.

Examples

Input

4
1 2 1 2

Output

Input

12
1 3 5 7 1 3 5 7 1 3 5 7

Output

#include<bits/stdc++.h>
using namespace std;
int a[201000];
int main(){
    int n;
    memset(a, 0, sizeof(a));
    int sum = 0;
    cin >> n;
    for(int i = 0; i <= n - 1; i++){
        int x;
        cin >> x;
        a[x]++;
        if(a[x] >= 2){
            sum++;
            a[x] -= 2;
        }
    }
    cout << sum / 2 << endl;
    return 0;
}